Method and apparatus for preventing premature ignition of electro-explosive devices



United States Patent [72] Inventor Richard R. Larson Ulster Park, New York [211 App]. No. 780,815 [22] Filed Dec. 3, 1968 [45] Patented Nov. 24, 1970 [73] Assign The United States of America as represented by the Secretary of the Air Force [54] METHOD AND APPARATUS FOR PREVENTING PREMATURE IGNITION 0F ELECTRO- EXPLOSIVE DEVICES 10 Claims, 2 Drawing Figs.

[52] US. Cl. 102/28 [51] Int. Cl. F42c 11/00, F42c 19/ 12 [50] Field ofSearch 102/28, 46, 86.5;86/l;29/623 [56] References Cited UNITED STATES PATENTS 2,696,191 12/1954 Sheehan 102/46X 2,977,878 4/1961 Kinkelet a1 102/28 Primary Examiner-Verlin R. Pendegrass Attorneys-Harry A. Herbert, Jr. and Arsen Tashjian ABSTRACT: A method and an apparatus for preventing the premature explosion, and the inadvertent breakage of bridge wire, in ignition systems, such as squibs and detonators, used in electroexplosive devices subjected to high linear and angular acceleration and high spin rates. The highly sensitive primer-type explosives of the system are compressed, in a suspended metallic cup, by a header assembly, which includes a hardened flat ended firing pin. A bridge wire is affixed to the bottom of the header assembly, abutting the explosives. The compression prevents explosion-causing acceleration vibrations from reaching the explosives and also prevents explosion-causing agitation of the explosives against each other. The position of the bridge wire, and its compressed state, result in the upward support of the bridge wire and eliminate its inadvertent breakage.

i ii R 5i e 5 W E? 55/ V I I n1 3/ 1 METHOD AND APPARATUS FORPREVENTING PREMATURE IGNITION OF ELECTRO-EXPLOSIVE DEVICES BACKGROIJND OF THE INVENTION This invention relates to electroexplosive devices subjected to high linear and angular acceleration and spin rates and, more particularly, to ignition systems of such devices.

In the interest of clarity, I prefer to discuss my invention, as applied to a detonator ignition system, in connection with prior art discussion of electro explosive devices.

Detonator ignition systems, generally, and systems of, that type usable in electroexplosive devices, specifically, are well known. Suffice it to say that in the conventional, and simplified embodiment, such systems include, as the critical component, a fuse, such as a fine electrically conductive wire or bridge having a diameter in the order of approximately .001 of an inch in diameter. Through such a fuse wire an electric current is passed, either directly by connection to an electrical source or indirectly by remote signal means. The application of current results in the explosion or substantially immediate vaporization of the bridge wire, with the resultant ignition of an adjacent, highly sensitive explosive'charge which, in turn, causes the explosion of a less sensitive, but more powerful explosive charge. Predetermined sequential detonation of charges continues until the explosive train is completed or is spent.

The present state of the art can be summarized by stating that efficient, highly reliable electroexplosive devices and ignition systems therefore, are available to accomplish purposes intended, provided that the environment in which they arev used is stable. However, conversely, if the environment is unstable, such as where there is a high "g" force acting on the device, there is no known reliable ignition system for electroexplosive devices.

The basic problem is two-fold. Firstly, the vibrations caused by the force or forces which are present in the unstable environment, and which are acting uponthe ignition system of the electroexplosive device, result in agitation of the highly sensitive primer or primer mix, and tend to, and often do, thereby prematurely detonate the primer or the primer mix. Secondly. in such an environment, because of the forcecaused vibrations andagitation, even if there is no premature detonation of the primer or primer mix, the thin bridge wire tends to, and often does, break prior to intended ignition or vaporization. The net result is that conventional ignition systems for electroexplosive devices are inefficient and highly unreliable in unstable environments.

The basic problem is further aggravated if the electroexplosive device must be used in the national interest in such an un-' stable environment. For example: the ignition system of an electroexplosive device in a cannon round must not function while the round, and of course the ignition system therein, is accelerating within the cannon barrel, but must function, upon command (from a proximity fuse, for example), or upon impact, after having left the barrel, is in flight, and is accelerating at high linear and angular rates (2.3., in excess of l00,000 gs") and at a high spin rate (e.g.,in excess of 100,000 rotations per minute). There is no known reliable ignition system for use under these conditions.

My invention solves this problem, and others similar thereto or related thereto, and thereby advances the state of the art.

SUMMARY OF THE INVENTION This invention relates to a method and an apparatus for preventing the premature explosion, or the inadvertent breakage of bridge wire, of ignition systems used in electroexplosive devices subjected to high linear and angular acceleration and high spin rates.

Therefore, an object of this invention is to prevent explosion in ignition systems of electroexplosive devices subjected to high linear and angular acceleration and high spin rates.

Obviously, another object of this invention is to prevent the breakage of the bridge wire element of an ignition system of an electroexplosive device subjected to high linear and angular acceleration and high spin rates.

Still another object of this invention is to provide a method and an apparatus which allows effective and highly reliable firing of the ignition system of electroexplosive devices subjected to high linear and angular acceleration and high spin rates.

These, and still other, objects of this invention will become readily apparent after a consideration of the description of the invention and reference to the drawings.

DESCRIPTION OF THE DRAWINGS FIG. I is a schematic representation, in vertical cross sec- DESCRIPTION OF THE PREFERRED EMBODIMENT As has been previously stated, in the interest of clarity, my invention will be described and discussed as applied to a detonator ignition system of an electroexplosive device. It is to be noted that such application is by way of illustration only and not by way of limitation.

With reference to FIG. 1, housing 111, which is preferably made of stainless steel, has an opening 12 through which is compressed and compacted a secondary-type detonatorexplosive powder 21, such as cyclotrimethylenetrinitramine (also known in the art as RDX"). The compaction pressure is in the order of 30,000 pounds per square inch. Compacted through opening 12, at or about the same pressure, and abutting explosive 21, is a primary-type detonator explosive powder 22, such as lead azide.

Still with reference to FIG. 1, metallic cup 31, preferably of stainless steel, has three openings, such as 31A and 318, in the bottom thereof. Cup 31 is fitted into housing 11 through'opening 12 and is positioned and suspended over, but is not touching or abutting, the compacted lead azide 22, with the external surface of the bottom of cup 31 facing the upper surface of the compacted lead azide 22. A paper disc 32, preferably of thin onion skin-type paper, is fitted within cup 31, with said paper disc 32 abutting the bottom of cup 31 and mating with the internal periphery of said cup 31. A primerassembly 40 which has a flat bottom that is configurated similar to, but is slightly smaller than, the internal configuration of cup 31, and with said header assembly 40 including: a flat ended hardened pin (i.e., hardpin") or firing pin 41; a hollow metallic tube 42 to which hardpin 41 is soft soldered 43; a metallic annularlike outer component 45 which is shorter than hardpin 41 and tube 42', and a glass seal 44 inter posed between the outer surface of tube 42 and the inner surface of outer component 45. A bridge wire 51, preferably of tungsten and ofa diameter'of .000135 inch, is affixed by suitable means, such as welding, on the bottom of header assembly 40 to outer component 44 and to tube 42, with one end of bridge wire 51 extending to, and abutting with, the flat end of hardpin 41. A primer-type ignition mix 61 of lead styphnate, nitrocellulose, and lacquer, is painted on, or otherwise applied to, the bottom of header assembly 40,including the exposed surface of bridge wire 51 affixed thereto. Then, header assembly 40 is positioned through opening 12 into housing 11, withignition mix 61 on the bottom of header assembly 40, abutting the top surface of percussion mix 33, and with tube 42 and hardpin 41 protruding from opening 12 of housing 11. That portion of housing 11 which extends beyond, i.e., above,

the top surface of outer component 44 and glass seal 45 is then crimpedover 13, and .on to, said top surface of outer com-' ponent 44. The results are: ignition-mix 61 and percussion mix 33 are placed under, and held in, high Compression, which prevents the agitation and unintended explosion of sensitive mixes 61 and 33; and, additionally and concurrently, bridge wire 51 is supported upwardly to such an extent that inadvertent breakage of bridge wire 51 is eliminated.

With reference to FIG. 2, the components shown therein include: housing 11; cup 31; annularlike outer component 45; glass seal 44; tube 42; soft solder 43; pin 41; and bridge wire 51.. Y

The apparatus is, then, lacquer sealed or varnished in its entirety (not shown), in the interest of safety and as a matter of preference.

MODE OF OPERATION OF THE PREFERRED EMBODIMENT The mode of operation of my invention is easily understood when said operation is described and discussed as applied to a detonator ignition system of an electroexplosive device, which is the embodiment shown in different views in FIGS. 1 and 2, wherein like reference characters designate the same component. It is again emphasized that such application is by way 'of illustration only, and not by way oflimitation.

used in elec'troexplosive devices subjected to high acceleration loads and high spin rates by placing under, and holding in, high compression the highlysensitive primer-type explosives 33 and 61, FIG. 1. This is accomplished by the use ofa cup 31,

FIG. 1, a header assembly 40, FIG. 1, with the highly sensitive I explosives 33 and 61, FIG. 1, being compressed between the bottom of header assembly 40, FIG. 1, and the internal bottom surface of suspended cup 31, FIG. 1. Vibrations are, thereby, prevented from reaching sensitive explosives 33 and 61', FIG. 1; and, additionally, the compression prevents explosives 33 and 61, FIG. 1, from agitating against each other. Further, the

' positioning of bridge wire 51, FIGS. land 2, coupled with the compression, results in the upward support of bridge wire 51, FIGS. 1 and 2, and the elimination of inadvertent breakage of bridge wire 51, FIGS. land 2. v

The energization of bridge wire 51, FIGS. 1 and 2, of my invention is conventional. That is, bridge wire .51, is energized by a command signal, such as from a proximity fuse, explodes and vaporizes as a result of the flow of electric current. This,

in turn, results in ignition and explosion, sequentially, of'

primer-type ignition mix 61, FIG. 1, and primer-type powder percussion mix 33, FIG. 1. This causes the combustion and burning of paper disc 32, FIG. I, with flames and debris passing through the three openings, such as 31A and 31B, of cup .31, thereby igniting, and resulting in the explosion of, compacted primary-type detonator explosive powder 22 and, thereafter, of compacted secondary-type detonator explosive powder 21. Thus, the desired timely detonation has been achieved.

In the event that impact or stab"detonation, rather than bridge wire detonation, is desired, bridge wire 51, FIG. 1, is not energized and, upon impact, hardened pin 41, FIGS. 1 and 2, crushes sensitive explosive mixes 33 and 61, FIG. 1, against cup 31, which acts as an anvil, resulting in: the detonation of explosive mixes 33 and 61, FIG. 1; the burning of paper disc 32, FIG. 1; the passing of flames and debris through three openings, such as 31A and 31B, of cup 31; and the resultant ignition, and sequential detonation, of explosives 22 and 21.

It is here to be noted that pin 41, FIGS. 1 and 2, is hardened and is soft soldered 43, FIGS. 1 and 2, in tube 42, so that thin column buckling, or bending from off center. will not result in a misflre. Additionally,.hardened pin 41, FIGS. 1 and 2, when used with captive friction cup 31. FIG. 1, results in two desirable firing characteristics: known length for pin 41 to travel before striking cup 31; and, known friction-generating mechanism not dependent upon the hardness of compacted explosive 22, FIG. 1.

While there has been shown and described the fundamental features of my invention, with regard to a preferred embodiment and with reference to a particular application, it is to be understood that various substitutions and omissions may be made by those skilled in the art, without departing from the spirit of the invention. For example: paper disc 32, FIG. 1, and openings, such as 31A and 3113, FIG. 1, of cup 31, and percus sion mix 33 may be omitted; a bridge wire, or fuse, of carbon. or other equivalent material, rather than of tungsten, may be used; a flat metallic disc may be used in place of cup 31; and, of course, different explosives, under different pressures may be used.

Iclaimz.

1. The method of preventing the premature explosion of, and the inadvertent breakage of bridge wire in, ignition systems used in electroexplosive devices subjected to high linear and angular acceleration and spin rates, comprising the steps of: i

a. affixing a bridge wire to the bottom of a header assembly of the ignition system;

b. painting a primer-type ignition mix on the bottom of the header assembly;

c. spreading a primer-type powder percussion mix in a metallic cup having the same configuration of, and being slightly larger than, the bottom of the header assembly;

positioning the metallic cup, facing upwardly and in a suspended mode, within the housing of the ignition system;

e. placing the header assembly, bottom down, in the metal-' lic cup; and

f. crimping the housing over, and on to, the header assembly, thereby compressing the primer-type explosive mixes and the bridge wire, disposed between the bottom of the header assembly and the cup.

2. Apparatus for preventing the premature explosion of, and the inadvertent breakage of bridge wire in, ignition systems used in electroexplosive devices subjected to high linear and angular acceleration and spin rates, comprising:

a. a cylindrical metallic housing open at one end and closed at the other end;

b. a secondary-type detonator explosive powder, compressed and compacted into said metallic housing and abutting the internal surface of the closed end of said metallic housing;

c. a primary-type detonator explosive powder, compressed and compacted into said metallic housing and abutting the top surface of the said compressed and compacted secondary-type detonator explosive powder;

d. a metallic cup, positioned within said metallic housing and suspended above said. compressed and compacted primary-type detonator explosive powder; a primer-type powder percussion mix spread within said metallic cup; f. a header assembly having a flat bottom that is configurated similar to, but is slightly smaller than, the internal configuration of said metallic cup, and including:

1. a flat ended hardened firing pin;

2. a hollow metallic tube to which said flat ended hardened firing pin is soft soldered;

, 3. a metallic 'annularlike outer component concentric with, and shorter than, said hollow metallic tube; and

4. a glass seal interposed between the outer surface of said hollow metallic tube and the inner surface of said metallic annularlike outer component;

g. a bridge wire affixed to the bottom of said header assembly and extending from said annularlike outer component to said flat ended hardened firing pin;

h. a primer-type ignition mix painted to the bottom of said header assembly, and covering the exposed portion of said bridge wire, with the outer surface of said ignition mix positioned to abut the top surface of said primer-type powder percussion mix spread within said metallic cup; and

i. with said cylindrical 'metallic housing beingcrimped, at the open end, over and on to said outer component of said header assembly, to compress said primer-type powder percussion mix and said primer-type ignition mix and said bridge wire, which are disposed between the bottom of said header assembly and said metallic cup.

3. The apparatus, as set forth in claim 2. wherein said cylindrical metallic housing is of stainless steel.

4. The apparatus. as set forth in claim 2. wherein said secondary-type detonator explosive powder is cyelotrimethylenetrinitramine.

5. The apparatus, asset forth in claim 2. wherein said primary-type detonatorexplosive powder is lead azide.

6. The apparatus, as set forth in claim .2. wherein said metal lic cup is ofstainless steel.

l. The apparatus. as set forth in claim 2, wherein said metallic cup has a plurality of openings in the bottom and a paper disc, within said cup, disposed between said openings and said primer-type powder percussion mix within said cup.

8. The apparatus, as set forth in claim 2. wherein said primer-type powder percussion mix includes lead styphnate. tetracene, lead azide, barium nitrate and antimony sulphide.

9. The apparatus, as set forth in claim 2, wherein said bridge wire is of tungsten.

l0. The apparatus. as set-forth in claim 2. wherein said primer-type ignition mix includes lead styphnate. nitrocellulose, and lacquer. 

